Effects of pulse duration on magnetostimulation thresholds

摘要: Purpose: Medical imaging techniques such as magnetic resonance and particle (MPI) utilize time-varying fields that are subject to magnetostimulation limits, which often limit the speed of process. Various human-subject experiments have studied amplitude frequency dependence these thresholds for gradient or homogeneous fields. Another contributing factor was shown be number cycles in a pulse, where decreased with longer pulses. The latter result demonstrated on two subjects only, at single 1.27 kHz. Hence, whether observed effect due pulse duration not specified. In addition, gradient-type field utilized; hence, same phenomenon applies remained unknown. Here, authors investigate limits 20-fold range frequencies using fields, ones used drive MPI. Methods: Magnetostimulation were measured arms six healthy (age: 27 ± 5 yr). Each experiment comprised testing eight different durations between 2 125 ms frequency, took approximately 30–40 min/subject. A total 34 performed three frequencies: 1.2, 5.7, 25.5 solenoid coil providing induce stimulation, real time. pre-emphasis based shaping method employed accurately control durations. Subjects reported stimulation via mouse click whenever they felt twitching/tingling sensation. sigmoid function fitted responses find threshold specific duration, whole procedure repeated all relevant durations. Results: The increasing (T pulse). For T pulse < 18 ms, significantly higher than longest (p 0.01, paired Wilcoxon signed-rank test). normalized (B Norm) vs curve agreed almost identically, indicating is independent operating frequency. At shortest (T pulse ≈ ms), 24% asymptotes. within 4% their asymptotic values > 20 ms. These trends well characterized (R 2 = 0.78) by stretched exponential given B Norm = 1 + α e − T pulse / β γ , parameters α 0.44, β 4.32, γ 0.60. Conclusions: This work shows first time decrease this Normalized identical short settle results emphasize importance matching conditions particular setup. Knowing safety factors critical time-efficiency systems